Baby bottle tooth decay (BBTD) continues to be a major cause of debilitating and costly dental pathology, affecting 6% of children under 3 years old. While inappropriate feeding habits are the most apparent risk factor, familial inoculation with a cariogenic microbial flora has been suggested as an additional contributing factor. Previous investigators have related total mutans streptococci (MS) counts to BBTD severity, but no one has completed a detailed characterization of the strains associated with this disease. We hypothesize that BBTD results from the proliferation of specific sub populations of Streptococcus mutans and that such strains may be obtained from the child's parents and/or siblings. When transferred to a child with inappropriate feeding habits, such strains may then proliferate and cause disease. This research seeks: (1) to utilize DNA fingerprinting and ribotyping to determine the genetic diversity of a large number of strains of MS previously isolated from developing nursing caries lesions and control sites in order to determine if there are specific subtypes of S. mu tans associated with BBTD, (2) to evaluate the presence of specific strains of S. mutans in the oral cavity of children with BBTD and their parents and sibs, and (3) to compare the MS associated with BBTD in different ethnic groups (Native American, African-American, Caucasian). The long-term goal of this research is to identify the sub- types of S. mutans which may be associated with BBTD. This information could then be used to identify and track specific strains for development of effective preventive and therapeutic strategies for BBTD. These strategies may include patient therapy prior to onset of disease, microbial therapy for families at risk and possibly prevention of recolonization of treated patients by passive immunization with appropriate antibodies.